Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/84—Biological processes
  • B01D53/85—Biological processes with gas-solid contact
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
  • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S95/00—Gas separation: processes
  • Y10S95/90—Solid sorbent
  • Y10S95/901—Activated carbon

Definitions

• This invention relates to a biofilter for use in the removal of contaminants from process gas streams.
• activated carbon can remove VOC's from air ⁇ treams at very high efficiencies
• carbon has only a limited capacity to adsorb any particular compound and quickly becomes saturated. Once the saturation limit is reached, the carbon bed will "break-through" and cease to be functional as a treatment system. When break-through occurs, the carbon bed must be regenerated or disposed of. Contaminated carbon is considered a hazardous waste under federal statutes and thus becomes very expensive to dispose of. Although some carbon companies offer regeneration facilities or on-site steam regeneration, the VOC's captured by the carbon still remain. Thus, when a VOC-saturated carbon bed is regenerated, condensed steam containing the VOC's removed from the carbon becomes hazardous waste.
• thermal incineration systems in which the process airstream containing VOC's is heated to above the decomposition temperature and maintained there for a certain residence time. This allows all of the organic contaminants contained in the process airstream to be destroyed.
• Thermal incineration is typically carried out using fluidized bed combustors, rotary kilns and special furnaces. Unfortunately, effective decomposition of contaminants present at the concentrations found in typical pollution control systems requires that large amounts of fuel be added to the contaminated airstream in order to achieve the necessary temperatures. Thermal incineration systems are also very expensive to maintain and operate and suffer from operation expenses which vary drastically with the fluctuating price of fuel supplies.
• catalytic incineration works on the same principle as thermal technologies, except that a catalyst is employed to lower the temperature at which the organic contaminants are destroyed.
• Many catalytic incinerators include heat exchangers to improve the process efficiency.
• catalytic incinerators still require large amounts of fuel or electricity when VOC concentrations ⁇ in the process airstream are low.
• Such systems also tend to be very expensive, complicated and subject to catalyst poisoning, a condition that occurs when the catalyst is transformed by a chemical reaction rather than facilitating it.
• lead contaminants act as a poison. Once poisoned, the catalysts must be replaced, adding further significant expenses to the operation of such incinerators.
• U.S. Patent No. 4,850,745 to Hater et al describes a system for treating soil contaminated with petroleum hydrocarbons.
• the system comprises an excavated cavity containing a layer of gravel which covers a bacterial culture capable of degrading petroleum hydrocarbons.
• a piping system capable of distributing nutrients directly to the cultures and a means for providing air flow through the area containing the cultures are provided as well.
• the present invention provides a modular biofilter for removing contaminants from an airstream. More specifically, the invention pertains to a modular unit having a series of stackable trays, some or all of which contain a gas-contacting medium that is adapted for the removal of contaminants such as VOCs from a process airstream.
• the stackable trays are formed of a molded polymeric material and are adapted to provide structural support for numerous layers of biologically active, gas-contacting material while also serving to provide an insulated vessel and an air distribution plenum.
• the trays may be rotationally molded and can be formed of recycled polymeric resins if desired.
• the present invention offers numerous advantages over biofiltration systems of the prior art.
• the modular nature of the stackable trays allows the number of trays, (and corresponding active surface area of the gas-contacting medium) to be increased or decreased with ease depending upon the requirements of the particular contamination site.
• the modular nature of the system allows the biofilter to be assembled on-site with a minimum of equipment and personnel needed to accomplish the assembly.
• each tray comprises a generally circular form having a vertical sidewall, and a bottom portion having a gas distribution plenum.
• the sidewall and bottom define a region for containing a gas-contacting medium such as a compost having a consortium of indigenous hydrocarbon degrading bacterial cultures.
• a gasket such as an O-ring, is provided to allow the trays to be stacked vertically in a sealed arrangement.
• the trays may also contain inlet and outlet ports, and ports for allowing sensors to monitor the interior conditions of the biofilter .
• biofilter formed of a series of identical trays to allow the unit to be readily transportable, easily assembled, and capable of being tailored to a specific application or waste site.
• FIG. 1 is an exploded view of one embodiment of the biofilter of present application.
• FIG. 2 is a top view of a biofilter tray.
• FIG. 3 is an elevation of a biofilter tray.
• FIG. 4 is a detailed elevation of an inlet port for a biofilter tray.
• FIG. 5 is a detailed elevation of an outlet port for a biofilter tray.
• FIG. 6 is a schematic representation of a modular biofilter configured to define a series flow path.
• FIG. 7 is a schematic representation of a biofilter used in the memorized pressure configuration.
• FIG. 8 is a schematic representation of a biofilter used in the parallel pressure configuration.
• FIG. 9 is a schematic representation of a biofilter used in the series-parallel pressure configuration.
• FIG. 10 is a schematic representation of a biofilter used in the series vacuum configuration.
• FIG. 11 is a schematic representation of a biofilter used the parallel vacuum configuration.
• FIG. 12 is a schematic representation of a biofilter used in the series-parallel vacuum configuration.
• FIG. 1 depicts one embodiment of a biofilter 10 of the present invention.
• a plurality of trays 12 each containing a gas-contacting medium 14 are stacked in a vertical arrangement.
• a gas-tight seal is achieved between each of the successive trays by means of O-rings 16 which are positioned between each tray 12 to provide a seal.
• a plurality of tie rods 18 are inserted through flanges 20 on each tray 12 to lock the stack of trays together. It is preferred that the tie rods 18 be threaded along their entire length to thereby allow a washer 22 and nut 24 to be positioned adjacent to the upper and lower surface of each flange 20 to distribute locking forces along the entire length of the biofilter stack.
• a cap 26 may be used to seal the top the assembly and a base or skid 28 may be used to provide reinforcement for the bottom of the assembly.
• the cap may comprise a screen or a perforated panel, but in the preferred embodiment, the cap comprises an inverted tray 12.
• the use of an inverted tray having a defined gas outlet allows the exit conditions of a process stream to easily monitored.
• Each of the trays includes a central hub 30. The hub assists in positioning the adjacent trays for purposes of sealing and alignment of flanges 20 to accommodate the tie rods 18.
• at least one tray includes an inlet for a process gas stream containing contaminants and at least one tray an outlet for the purified gas stream.
• the gas-contacting medium comprises a substrate that includes numerous microbial cultures capable of metabolizing contaminants contained in the air stream.
• Ordinary compost such as is widely available from numerous landfills and composting facilities, includes a consortium of indigenous hydrocarbon degraders, and is thus well-suited for use as the gas contacting medium of the present invention.
• the primary volatile components of gasoline (benzene, toluene, ethylbenzene and xylene) may be readily metabolized by many of the hydrocarbon-consuming microbial cultures found in compost, including Pseudomonas putida and P ⁇ eudomonas aerugino ⁇ a.
• the bacteria contained in compost is also capable of consuming, among other organic solvents, chlorinated solvents such as trichloroethylene (TCE) .
• TCE trichloroethylene
• a compost mixture having components adapted to increase the residence time of the process gas may be used.
• a mixture comprising compost and various clays is substituted for straight compost.
• the mixture (referred to as a 60:30:10 mix), comprises 60% by weight compost, 30% by weight Fuller's Earth (a non-colloidal attapulgite clay, preferably having an 80/50 mesh size), and 10% by weight PT1E (an organophilic clay that is, a clay that readily absorbs organic compounds, adapted to absorb hydrocarbons, available from Bentec Inc., Ferndale, Michigan).
• a small amount, preferably less than 1% by weight, of a nutrient for the bacteria may be used.
• a preferred nutrient is Max Bac, a timed release bioremediation nutrient source available from Grace Sierra Horticultural Products Company of Milpitas, California.
• the invention is not intended to be limited to the use of specific gas-contacting media but rather, is intended to include any of a wide variety of media for removing contaminants from a gas stream.
• the composition of the gas-contacting medium may differ from tray to tray.
• the invention is not intended to be limited solely to the use of gas-contacting media containing bacteria, but rather may include non-bacterial media as well.
• at least one tray of the biofilter may include activated carbon to provide chemical "polishing" of the decontaminated gas stream.
• the gas-contacting media is a substrate containing a microbial culture
• the substrate preferably comprises the 60:30:10 mix described above.
• This material is particularly desirable since it is relatively inert, yet contains a large supply of nutrients as well as a large surface area.
• an inert packing such as pine bark, can be positioned below the medium to diffuse the flow of the process gas stream and prevent channeling.
• activated carbon can be added directly to the medium to increase the effective residence time of any contaminants that are present in a low concentration or are metabolized by the microbial cultures at a slower rate.
• FIGS. 2 and 3 depict one embodiment of a tray 12 for use in the biofilter.
• the tray 12 preferably has a circular configuration with a peripheral side wall 32 extending upwardly from a bottom portion 34. Although the tray may be formed to virtually any size, in one preferred embodiment, the tray has a diameter of between 50 and 60 inches.
• FIG. 2 which depicts a top-view of the tray, it can be seen that the tray bottom 34 includes a plurality of upwardly extending, parallel ribs 36 containing numerous outlet holes 38. The ribs define the upper surface of a plenum through which a contaminated gas stream may be flowed. The gas stream exits the plenum through the outlet holes 38 and into the gas-contacting medium contained in the tray.
• the details of the plenum as well as the gas inlet and outlet are described in more detail in the description of FIG. 3.
• the tray also includes a central hub 30 which extends upwardly from the center of the bottom portion 34 and has a number of alignment flanges 40 that allow numerous trays to be fitted together with their external flanges 20 in linear alignment.
• the bottom portion 34 of the tray also includes numerous circular drains 42 which, if perforated, allow any liquids present in the filter to drain to its lowermost portion.
• the drains 42 also act as pillars, thereby providing structural support to the bottom portion 34 of the tray.
• a sealing groove 44 is provided in the upper surface of the peripheral wall 32 to accommodate an O-ring which is used to facilitate the seal between adjacent trays.
• a gas inlet 46 and a gas outlet 48 are also provided in the peripheral side wall.
• the tray is fabricated of a polymeric material which has been molded using a rotation molding technique.
• the tray is an essentially hollow body, and such hollow bodies are well suited to fabrication using ' rotational molding methods.
• the polymeric material comprising the tray preferably comprises a high density polyethylene and most preferably comprises a recycled polymer.
• One additional advantage of the rotational molding method is that the tray may be fabricated in its entirety without the need to later attach parts such as the flanges 20 or the central hub 30. Additionally, the molding technique allows text and symbols, such as assembly and use instructions, company logos, and the like, to be molded directly into the side wall for permanent viewing.
• FIG. 3 A cutaway elevation of the tray is presented in FIG. 3.
• the side wall 32 and bottom portion 34 of the tray are hollow, thereby defining a plenum through which a process stream, such as a contaminated gas stream may enter the tray interior.
• the plenum comprises a plurality of ribs 36 extending along the bottom in a parallel relationship.
• a view that is not in a direction parallel to the ribs the plenum extends into the side wall 32 and communicates with both the ribs 36 and the central hub 30.
• the left side of FIG. 3 shows a view that is in a direction parallel to that of the ribs. This view allows the drains 42 to be seen.
• the bottom portion 34 of the tray includes, around its lower circumference, a sealing channel 52 which is designed to engage the upper portion of the peripheral wall of an adjacent tray.
• the upper portion of the peripheral wall includes a groove 44 for seating an O-ring thereby allowing a gas-tight seal to be achieved between adjacent trays.
• the bottom portion 34 also includes a hub engagement zone 54 adapted to engage the upper portion of the hub 30 of an adjacent tray.
• a gas stream can enter the plenum by either of two paths, depending upon whether the stream is being flowed through the biofilter trays either in series or in parallel. In the series configuration, the process stream enters the plenum of -li ⁇
• the lowermost tray through an inlet port 46 (described in detail in FIG. 4), flows into the ribs 36 and then exits the ribs into the gas-contacting medium through the perforations 38.
• the bottom portions 34 of all trays above the bottom tray include perforations in the wall defining the bottom of the plenum, thereby allowing process gas ⁇ to flow from the gas-contacting medium of the tray below into the plenum of the adjacent, upper tray and then into the gas-contacting medium of that adjacent upper tray.
• the gas stream Upon reaching the uppermost tray, the gas stream is allowed to exit the biofilter through a gas outlet in the peripheral side wall that communicates with the space above the gas-contacting medium.
• each tray includes a process stream inlet 46 positioned in the side wall through with gas may enter the plenum.
• Each tray also includes a gas outlet 48 positioned in the side wall and communicating with the space above the gas-contacting medium to thereby allow the process stream to exit the tray directly rather than flowing into an adjacent tray.
• FIG. 4 is a cutaway elevation of an inlet port 46.
• the inlet port is molded directly into the peripheral sidewall 32 and includes a threaded wall 56 and a blind wall 58. If it is desired to have a proces ⁇ ⁇ tream enter the inlet port 46 of a given tray and thu ⁇ enter the plenum of that tray, the blind wall 58 is either removed or perforated and a gas supply line can be screwed to the tray via the threaded wall 56. Gas entering the inlet port 46 flows into the tray plenum and into the ga ⁇ -contacting medium through the perforations 38 in the ribs 36.
• FIG. 5 depicts a gas outlet port 48 from the tray.
• the port is designed to allow fluid communication between the space above the gas-contacting medium and the outside of the tray.
• the port is isolated from the plenum to prevent inlet and outlet gas ⁇ es from mixing.
• the port is molded to include a pair of removable sealing walls 62, 64 that, when positioned in the port, render it inoperative. Upon removal of the sealing walls 62, 64, communication between the interior of the tray and the exterior of the tray through the side wall is achieved.
• the tray may additionally include a plurality of post ⁇ 66 molded into the side wall 32 to provide additional structural support to the side wall.
• FIG. 6 The operation of one embodiment of a biofilter is depicted schematically in FIG. 6.
• four trays 12 each containing a gas-contacting medium 14 are stacked together and sealed about their peripheral walls 32 using O-rings 16.
• a fifth tray that has been inverted relative to the others, acts as the upper seal of the biofilter.
• a gas stream is flowed into the plenum of the bottom tray through that tray's inlet port 46. The gas then flows through the ribs of the bottom tray, out through the perforations therein and into the lowermost gas-contacting medium 14. Upon exiting the medium, the gas stream enters the plenum of the adjacent tray through perforations in the bottom of the plenum of the adjacent tray.
• the gas then exits the plenum into that tray's gas-contacting medium. This process continues until the gas reaches the space above the uppermost gas-contacting medium, this space being defined by the inverted, uppermost tray.
• the cleaned proces ⁇ gas is then allowed to exit the tray through its exit port 48.
• the interior conditions of the biofilter may be monitored and controlled by numerous methods.
• probes 70 for determining variables such as temperature, moisture content, pH, flow rates and the like may be inserted into the biofilter interior either through the inlet 46 or outlet 48 ports (whether such ports are used or not) or, through additional ports 72 that may optionally be provided in the sidewall 32 of each tray.
• the probes 70 may be connected to a monitoring and reacting device, such as a computer, that can modify the interior conditions in response to parameter fluctuations, quality of the inlet and outlet process streams, and the like.
• the flow rate of the process stream can be decreased to increase residence time of the gas in the filter, thereby allowing the microbial cultures a longer time to metabolize the contaminant.
• other parameters such as temperature, moisture content, pH, and the like may be controlled as well.
• FIGS. 7-12 Various configurations for supplying a process gas to the biofilter an flowing it therethrough are depicted schematically in FIGS. 7-12.
• a contaminated process gas stream is drawn from contaminated soil 100 into a perforated pipe 102 via an explosion proof blower 106.
• a moisture separator 104 removes moisture from the process stream prior to entering the blower.
• a moisturizer 108 capable of adjusting the temperature and humidity of the process stream is used to treat the stream before it enters the biofilter 10.
• the moisturizer preferably raise ⁇ the humidity level of the proce ⁇ S stream to approximately 100%. In so doing, the temperature of the process stream may be readily controlled due to the increased heat capacity of humid gas streams.
• the stream flows from the lowermost portion to the uppermost portion of the filter through the trays in series, ultimately exiting the filter into either the atmosphere or into further processing equipment by outlet tube 110.
• the system is configured identically to the series pressure configuration up to the exit of the moisturizer.
• the process stream is flowed into an inlet manifold 112 that causes the process stream to be split and flowed into the plenum of each tray independently and isolated from the other process streams.
• Each tray also has an outlet port connected to an outlet manifold 114 in which the process streams, each flowed through a single tray, are recombined and allowed to vent into the atmosphere or to subsequent processing equipment.
• the purified gas stream exits a tray through a tray sidewall, rather than through the top of the tray, it is preferred that the purified gas stream be withdrawn from above the top of the gas-contacting medium.
• the tray may be designed to have an outlet positioned in the sidewall above the fill level of the gas-contacting medium, or in the alternative, a pipe elbow may be installed on the tray-interior side of the outlet port to act as a snorkel to withdraw the process stream from above the gas-contacting medium surface.
• FIG. 9 the series-parallel pressure configuration, is a hybrid of the systems depicted in FIGS. 7 and 8.
• the front end of the system up to the exit of the moisturizer is identical to that shown in FIGS. 7 and 8.
• the process stream Upon reaching the biofilter 10, the process stream enters a partial inlet manifold 116 which provides gas directly into the plenums of every other tray.
• Each proces ⁇ stream flows in series from a first tray into a second tray and out through the outlet port of each second tray into a partial outlet manifold 118 where the processed gas stream is recombined and sent into the atmosphere or flowed to subsequent processing equipment.
• This configuration thus allows the gas stream to split into parallel streams which are each flowed in series into multiple trays.
• FIGS. 10-12 differ from those of FIGS. 7-9 in that in the latter figures, the proces ⁇ ⁇ trea is flowed through the biofilter by means of a vacuum rather than by pressure.
• the series vacuum configuration a process stream is drawn from contaminated soil 100 through a perforated pipe 102 and directly into a moisturizer 108. From the moisturizer, the process stream is flowed directly into the inlet port of the lowermost tray of a biofilter 10 and allowed to proceed in series up through the biofilter exiting at its uppermost tray.
• the purified proces ⁇ stream Upon exiting the biofilter, the purified proces ⁇ stream is flowed through a moisture separator 104 and subsequently through an explosion proof blower 106 that provides the suction force drawing the process stream through the system. Upon exiting the blower 106 the process stream is vented into the atmosphere or flowed into subsequent processing equipment.
• FIG. 11 the parallel vacuum configuration, is similar to the configuration of FIG. 8 with the exception that the process stream is drawn from the soil and through the biofilter 10 by means of a vacuum created by the blower 106 positioned downstream of the outlet of the biofilter.
• an inlet manifold 112 and an outlet manifold 114 are used to first separate and then recombine process streams.
• the series-parallel vacuum configuration differs from FIG. 9 in that the process stream is drawn from the soil into the biofilter also by means of a suction force created by positioning the blower 106 downstream of the outlet port of the biofilter 10.
• a partial inlet manifold 116 and a partial outlet manifold 118 are used to split and then recombine the process stream.
• the invention is not intended to be limited to the use of a single biofilter. Rather, depending upon the specific requirements of a contamination site, numerous biofilters of the types de ⁇ cribed above may be interconnected either in series or in parallel. Furthermore, the invention is not intended to relate to configurations in which the process stream moves through a tray series only from the lowermost tray upward. Rather, the system may, if desired, be configured to allow downward or multi-directional gas flow. Examples

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• Engineering & Computer Science (AREA)
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• Biomedical Technology (AREA)
• Environmental & Geological Engineering (AREA)
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• Life Sciences & Earth Sciences (AREA)
• Molecular Biology (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Treating Waste Gases (AREA)
• Separation Of Gases By Adsorption (AREA)

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• 1993
  • 1993-09-16 AU AU49253/93A patent/AU4925393A/en not_active Abandoned
  • 1993-09-16 JP JP6508306A patent/JPH08501251A/ja active Pending
  • 1993-09-16 EP EP93921621A patent/EP0660745A1/de not_active Withdrawn
  • 1993-09-16 WO PCT/US1993/008747 patent/WO1994006539A1/en not_active Ceased
  • 1993-12-10 US US08/165,517 patent/US5595910A/en not_active Expired - Lifetime
• 1995
  • 1995-06-07 US US08/484,350 patent/US5656494A/en not_active Expired - Fee Related

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